Influence of Surface Roughness on Turbine Nozzle Profile Loss and Secondary Loss

Abstract

The effects of surface roughness of both nozzle and end-wall on a turbine nozzle performance were investigated experimentally using liner cascade wind tunnel facility under the Reynolds number (Re) condition of Re = 0.3∼1.0 × 106. With buffing, milling, sand blasting and shot blasting, the total of seven levels of the model surface roughness were realized. In order to clarify the effect of the nozzle surface roughness on the profile loss, total pressure losses were measured using three-hole probe for different levels of the surface roughness. It became clear the nozzle profile loss increases as Reynolds number increases for larger roughness group. In addition, it appeared the profile loss depends on not only maximum value of the surface roughness but also roughness conditions. In order to examine the effect of surface roughness on the secondary flow loss, spatial total pressure field of the secondary flow region was measured using three-hole probe for the cases of smooth or rough nozzle surface with smooth or rough end-wall. The secondary flow structures were recognized at the 5∼10% span-wise height region of the suction surface of the nozzle for all cases. With increasing the nozzle surface roughness, not only the profile loss but also net secondary flow loss increases, which is defined as the difference between the total pressure loss and the profile loss in the secondary flow region. However, increase of the end-wall roughness has higher effect on the net secondary flow loss increase. Difference of the effect between the nozzle surface roughness and the end-wall roughness on the nozzle secondary flow loss was discussed.

Experimental Investigation of the Aerodynamic Effect of Local Surface Roughness on a Turbine Blade

“…In terms of similar results as the studies previously mentioned, the conducted studies can be mainly seperated into two parts: The first part are the studies using sand grains on turbine blades in cascades or rotating test rigs [3][4][5][6][7][8][10][11][12][13][14]. The second part are studies that investigated the effect of real surface roughness by deterioration or machining of the blades [9,[15][16][17][18][19][20][21]. The general outcome is that surface roughness can increase losses by up to 40% and only in (rare) special cases has a beneficial influence by supressing laminar separation bubbles [22][23][24].…”

Gas Turbine Engine Performance Estimation and Prediction

“…Several research works have investigated the relation between fault modes and consequent degradation symptoms of the turbines [168][169][170][171], whereas fewer works have growth of symptoms 1 st 15 th 10 th studied the growth of the degradation symptoms over time [1]. Beside the effect of time, it is expected to experience faster degradation under higher levels of the GTE power, which lead to harsher operating condition for the components.…”

“…The dominant fault modes in the nozzle and the turbine section are known as: a) increase of the surface roughness in the nozzle vanes and the turbine blades[165], b) increase of the tip clearance in the turbine, and c) material removal and deformation of the profile[166,167]. The fault modes manifest their symptoms as deviations in the turbine performance map, i.e., under a constant operating condition, all the fault modes lead to loss of isentropic efficiency in the turbine, whereas the tip clearance and material removal from the profile lead to increase of the mass flow[168][169][170][171]. When the GTE is running, the only directly measurable fault is the tip clearance using advanced instrumentation, while the other two fault modes remain inaccessible for direct measurement.…”